The present invention relates to inductive power transmitters, electrical conduits therefor, related equipment and related methods.
It is desirable for electronic devices to meet electromagnetic compatibility (EMC) regulations. By way of example, one European such regulation is referred to as EN55011:1998 together with A1:1999 (denoting an EU standard plus an amendment thereto), and one American such regulation is referred to as ANSI C63.4-2001 (denoting a US standard). One part of such regulations, or the like, governs unwanted signals (so-called “conducted emissions”) that may be conducted back into a mains supply. Wireless transmitting devices deliberately emit radiation and it is desirable to ensure that this radiation (or spurious tones thereof) is not picked up by the mains cable and conducted back into the mains supply.
Devices, such as inductive power transmitters, designed to transmit power wirelessly to portable electrical or electronic devices (or equipment used in the vicinity thereof) can be especially prone to pick-up in their mains cables. The fundamental frequency of electromagnetic fields generated by such transmitters is generally lower than that of data transmitters, but the power transmitted is generally higher. Such transmitters may generate relatively high magnetic fields in the vicinity of their mains cables. Furthermore, nonlinearities present in the system (e.g. in the rectification circuitry within the portable device itself) can result in harmonics and other spurious tones, which exacerbate the problem.
One way to mitigate this problem is to use shielded mains cable. However, shielded cable is expensive and its use may be prohibitively expensive for low-cost consumer applications.